Systems for tracking moving objects have utility in various technical fields. Thus, they can be used to control and calibrate robotic devices, inspect large critical parts such as dish antennas, air frames and propellers, and control machine tool operations and laser welding. In addition to merely tracking the moving object, these systems typically utilize distance measuring devices, such as laser interferometers, to determine the distance at any point in time of the object relative to a reference location. The precise location of the moving object in a volume is typically determined using three tracking and distance measuring devices and the well-known trilateration method. Adding additional structure can also provide the relative angle of the moving object.
While considerable work has been done in the prior art to develop these systems to a high degree of accuracy, the typical prior art systems have numerous disadvantages. One type of system utilizes gimballed flat mirrors to steer beams of radiation and servo-controlled motors to vary the angular position of the mirrors relative to the object. These gimballed mirrors, however, are accurate only to about 20-50 microns with respect to a volume of about 100 cubic meters. The accuracy of these systems is limited by bearing and shaft alignment errors, known as run out errors, and by the initial alignment error of the laser beam and the precise center of the mirror. Moreover, these gimballed mirrors afford only limited tilt angles and require frequent recalibration.
Additional systems utilize reflective pellicles which are formed from very thin reflecting membranes, the thickness being on the order of several microns. However, these pellicles are not rugged and are difficult to work with since they tend to vibrate.
Examples of these prior art systems are disclosed in the following U.S. Pat. Nos. 4,436,417 to Hutchin; 4,457,625 to Greenleaf et al; and 4,621,926 to Merry et al, the disclosures of which are hereby incorporated by reference.
Thus, there is a continuing need to provide improved tracking and distance measuring devices of high accuracy.